The present invention generally relates to position sensing devices and methods and, more particularly, to a position sensing device and method incorporated into an optical scanning device for determining the position of the optical scanning device relative to a smooth surface.
Hand-held scanning devices are portable imaging devices that generate machine-readable image data, (which may be referred to herein simply as xe2x80x9cimage dataxe2x80x9d) representative of an image of an object. Generating image data representative of an image of an object is sometimes referred to as xe2x80x9cimagingxe2x80x9d or xe2x80x9cscanningxe2x80x9d the object. Some scanning devices generate image data representative of a narrow xe2x80x9cscan linexe2x80x9d portion of the object being imaged. During the imaging process, the scanning device is moved relative to the object being imaged. As the scanning device is moved relative to the object, the scanning device generates image data representative of a plurality of sequential scan line portions of the image of the object. The image of the object is, accordingly, represented by image data of the cumulation of sequential scan line portions, similar to the image of the object represented by a conventional video display.
Examples of hand-held scanning devices are described in the following United States patents and patent applications, which are all hereby incorporated by reference for all that is disclosed therein: U.S. Pat. No. 5,552,597 of McConica for HAND-HELD SCANNER HAVING ADJUSTABLE LIGHT PATH; U.S. Pat. No. 5,646,394 of Steinle for IMAGING DEVICE WITH BEAM STEERING CAPABILITY; U.S. Pat. No. 5,646,402 of Khovaylo et al. for EXPANDABLE HAND-HELD SCANNING DEVICE; U.S. Pat. No. 5,723,859 of Kerschner et al. for LINE CONTACT HAND-HELD SCANNING DEVICE AND METHOD HAVING A LIGHT PATH SUBSTANTIALLY PERPENDICULAR TO THE ORIENTATION OF THE OBJECT AT A LINE PORTION; Ser. No. 09/120,641 (U.S. Pat. No. 6,043,503) of Sims et al. for HAND HELD SCANNING DEVICE filed on Jul. 29, 1998; and Ser. No. 09/120,637 (now abandoned) of Sims et al. for HAND HELD SCANNING DEVICE filed on Jul. 30, 1998.
In some scanning devices, the image of the scan line portion of the object is focused onto a linear array of photodetector elements, sometimes referred to herein simply as photodetectors. The photodetectors may, as an example, be mounted to a plurality of linearly arranged electronic segments such as xe2x80x9ccontact image sensorsxe2x80x9d as are known in the art. The photodetectors may also be etched into a single semiconductor as is common with a charge-coupled device. The individual photodetectors generate image data representative of discrete portions of the image of the scan line portion of the object. The image data may, as an example, be voltages wherein a relatively high voltage represents a relatively high intensity of light received by a photodetector and a relatively low voltage represents a relatively low light intensity received by a photodetector.
The image data generated by the photodetectors is transmitted to a processor. One of the functions of the processor is to create a data base or similar electronic structure that indicates the positions of the scan lines relative to the positions on the object from where the scan lines were generated. Alternatively, the data base may indicate the locations of the scan lines relative to each other. The data stored in the data base and the image data are used by the processor to replicate the image of the object. As an example, in the situation where the scanning device is generating image data representing a two-dimensional object, such as text printed on a sheet of paper, the hand-held scanning device may be moved in any direction on the paper. Accordingly, the scan line portions may be generated from virtually any location on the paper, which causes the image data representing the image of the object to consist of a plurality of scan line portions that may be skewed over the surface of the paper. In order to accurately replicate the image of the object, the hand held scanning device uses the data stored in the data base to determine the proper placement of the scan line portions of the image text printed on the paper. The processor may then create an electronic image of the text printed on the paper by known processing techniques, e.g., stitching software.
A problem replicating the image of the object is encountered if the velocity, position, or direction of movement of the scanning device relative to the object becomes unknown during the scanning process. For example, if the scanning device is imaging one thousand scan line portions of the image of the object per second and the scanning device is moving along a single axis at a constant rate of one inch per second relative to the object, each scan line represents one one-thousandth of an inch of the image of the object. If the correct velocity and thus, position, of the scanning device relative to the object has been conveyed to the processor, the processor will create a data base indicating that each scan line represents one one-thousandth of an inch of the image of the object. Alternatively, the processor will indicate that each scan line is located one one-thousandth of an inch from an adjacent scan line. Based on the image data and the data stored in the data base, the processor may accurately replicate the image of the object. If, however, the velocity of the scanning device relative to the object is decreased and the decreased velocity is not conveyed to the processor, the processor will continue to process the image data as though each scan line represents one one-thousandth of an inch of the object. Each scan line, however, will represent less than one one-thousandth of an inch of the object. Accordingly, the replicated image of the object will be compressed. If, on the other hand, the velocity of the scanning device relative to the object is increased and the increased velocity is not conveyed to the processor, the replicated image of the object will be expanded.
Accurately replicating an image of an object when either the velocity or position of the scanning device relative to the object becomes unknown is impossible. If the position or velocity is not known, the processor will not know where the scanning device is located relative to the object as the scan lines are being generated. Accordingly, the processor will not be able to properly place the scan line portions relative to each other so as to replicate the image of the object. This problem is exacerbated in hand-held scanning devices where the scan lines may be generated from anywhere on the object and are often skewed over the surface of the object.
In order to overcome these problems, scanning devices use position sensors to detect the position of the scanning device relative to the object. The position sensors output position information pertaining to the position of the scanning device relative to the object as the scan line portions of the image of the object are being generated. This position information is conveyed to the processor where it is incorporated into the above-described data base that is used for position sensing.
Some scanning devices have an optical sensor affixed to the scanning device to determine the position of the scanning device relative to the object being imaged. The optical sensor periodically generates image data representative of a small two-dimensional area of the object being imaged. A processor receives this image data and identifies distinct features in the image of the object. In the example where the object is text printed on a sheet of paper, the distinct features may be inherent irregularities in the surface of the paper. The positions of these distinct features relative to the optical sensor are stored in a memory device. As the scanning device is moved relative to the object, the positions of these distinct features move relative to the optical sensor. The processor compares the new positions of these distinct features to the positions stored in the memory device. Based on these comparisons, the processor is able to determine the position, direction of movement, and velocity of the scanning device to which the optical sensor is affixed relative to the object. Accordingly, the processor is able to create the above-described data base because the locations of the scan line portions of the image of the object relative to each other may be readily determined. It should be noted that some scanning devices use a plurality of optical sensors to better determine the position of the optical sensor relative to the object being imaged. Examples of imaging area portions of a surface to determine the position of an optical scanning device relative to the surface are further described in the following U.S. Pat. No.: 5,644,139 of Allen et al. for NAVIGATION TECHNIQUE FOR DETECTING MOVEMENT OF NAVIGATION SENSORS RELATIVE TO AN OBJECT; and U.S. Pat. No. 5,578,813 of Allen et al. for FREEHAND IMAGE SCANNING DEVICE WHICH COMPENSATES FOR NON-LINEAR MOVEMENT, which are both hereby incorporated by reference for all that is disclosed therein.
The images of some surfaces, however, do not have distinct features that are able to be imaged for purposes of determining the positions of the scanning device relative to the surfaces. For example, in the case where the surface of the object being imaged is smooth or glossy, such as with some photographs and magazine covers, there typically are not enough suitable distinct features in the image of the surface to achieve the above-described position sensing. Accordingly, the processor is unable to determine the location of the scanning device relative to the surface being imaged. Thus, the processor is unable to determine the locations from which the scan line portions are imaged. This results in the scanning device being unable to generate image data representative of these smooth or glossy surfaces.
Therefore, a need exists for an optical positioning system that is able to accurately determine its position relative to an object that has a smooth or glossy surface.
A method and system for determining the position of a first object relative to a second object are disclosed herein. The method may comprise providing a sheet wherein the sheet has a first surface that is contoured and a second surface that may or may not be contoured. The second surface of the sheet may be placed adjacent a surface of the second object so as to substantially conform to the surface of the second object. The method may further comprise providing an imaging system fixedly associated with the first object. The imaging system may be placed adjacent the sheet first surface and may be moved along with the first object relative to the sheet first surface. The imaging system images planar portions of the sheet first surface and identifies distinct features on the first surface and, additionally, identifies the locations of the images of the distinct features relative to the imaging system. As the first object and the imaging system are moved relative to the sheet first surface, the images of the distinct features relative to the imaging system move accordingly. The imaging system measures the amount and direction of the relative movement between the imaging system and images of the distinct features. The relative movement between the first object and the second object is then readily determined, which in turn, yields the position of the first object relative to the second object.